Belts of the abovementioned type are of exceptional importance in particular in drive engineering. These belts are also termed drive belts or force-transmission belts, and can be flat belts, V-belts, V-ribbed belts, toothed belts, or composite cables. The force-transmission zone here provides the belt-drive function. Patent literature to which reference is in particular made in this connection is: DE 38 23 157 A1, U.S. Pat. Nos. 7,128,674, 8,262,523, DE 10 2007 062 285 A1, DE 10 2008 012 044 A1, DE 10 2009 044 153 A1, U.S. Pat. No. 5,807,194, WO 2005/080821 A1, United States patent application publication 2008/0032837, United States patent application publication 2011/0129647, U.S. Pat. Nos. 3,981,206, 5,417,618, and 6,491,598.
It is moreover known that belts can be used to convey materials, other terms used for belts of this type being transport belts or conveyor belts. The outer layer, as belt backing, then provides the outer surface on the loadbearing side for the material to be conveyed. The substructure is then the outer surface in contact with a drive drum on the drive side.
The elasticity of a belt is achieved in that the main belt structure, and therefore the outer layer and the substructure, are composed of a polymeric material with elastic properties, particular groups of materials that may be mentioned here being elastomers and thermoplastic elastomers.
Materials of particular importance are elastomers based on a crosslinked rubber mixture comprising at least one rubber component and mixture ingredients. A particular rubber component used is ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), hydrogenated or partially hydrogenated nitrile rubber (HNBR), fluororubber (FKM), natural rubber (NR), chloroprene rubber (CR), styrene-butadiene rubber (SBR), butadiene rubber (BR), or polyurethane (PU), these being unblended or blended with at least one other rubber component, in particular with one of the abovementioned types of rubber, for example in the form of an EPM/EPDM or SBR/BR blend. A material of particular importance here is HNBR, EPM, EPDM, PU or an EPM/EPDM blend. The mixture ingredients comprise at least one crosslinking agent or one crosslinking agent system (crosslinking agent and accelerator). Other mixture ingredients are mostly a filler and/or a processing aid, and/or a plasticizer and/or an ageing inhibitor, and also optionally other additional substances, for example fibers for reinforcement purposes, and color pigments. Reference is made in this connection to the general prior art in rubber mixture technology.
The belt has an embedded tension-member system composed of at least one tension member running in the longitudinal direction of the belt. There are mostly a plurality of tension members forming a tension-member-system layer. A tension member composed of a cord structure is of particular importance here, and in this connection the prior art provides configurations using various materials. The significant types of materials are: steel, polyamide (PA), aramid, polyester, carbon, basalt, polyetheretherketone (PEEK), polyethylene terephthalate (PET), polybenzoxazole (PBO), and polyethylene 2,6-naphthalate (PEN).
In particular the force-transmission zone of a belt for drive engineering is provided with an abrasion-resistant coating which also serves for noise reduction and can moreover also be oil-resistant. A flock overlay, in particular in the form of a cotton flock or aramid flock, can be used here, or a thin elastic polymer layer filled with fibers (for example, aramid fibers), a textile overlay, in particular in the form of a woven or knitted fabric, or a film (for example, PTFE film), or a film composite (for example, PA-PTFE film). Woven fabric is of particular importance. The coatings mentioned here are mostly treated to promote adhesion, for example with a resorcinol-formaldehyde latex (RFL), on the side in contact with the main belt structure, in particular the side in contact with the substructure thereof.
The prior art for the treatment of the tension-member system is now described in more detail below.
U.S. Pat. No. 5,807,194 presents a toothed belt in which the main belt structure is composed of a cast polyurethane. The embedded tension-member system composed of a cord structure is composed of carbon fibers, the cord being subjected to a particular process. When the belt is cast, only a portion of the cavities in the tension-member system are filled with the polyurethane casting composition. It is disadvantageous that a precondition of this type of treatment of the tension-member system with polyurethane is that the main belt structure is likewise composed of a polyurethane of identical composition. No attention is therefore given to the different properties of the carbon tension-member system and of the main belt structure.
United States patent application publication 2011/0129647 describes a belt, the tension-member system of which is composed of a cord structure and has been treated with a crosslinked polyurethane. The degree of filling of the cavities in the tension-member system with the crosslinked polyurethane is preferably from 20% to 100%. A polyurethane prepolymer is formed by selecting polyols from polyester polyols, polycarbonate polyols, and polyether polyols as component A and reacting these with diisocyanates as component B. The resultant polyurethane prepolymer can then be crosslinked with a diamine and/or with water, in particular with water.
United States patent application publication 2011/0129647 also presents a treatment process for the tension-member system which is an upstream stage, specifically being what is known as a “two-bath method”. The tension-member system here is impregnated with a mixture of a polyurethane prepolymer and an inert solvent/dispersion medium, whereupon the cavities in the tension-member system are at least to some extent filled with the mixture. This is followed by a drying procedure. Crosslinking with water then takes place. The belt is then produced with the tension-member system thus treated.
During the handling and processing of tension-member systems it is possible that individual filaments separate from the tension-member system, with resultant impairment of the mechanical properties of the tension-member system. In the case of tension-member systems made of electrically conductive filaments, for example carbon fibers, there is the additional problem that complicated shielding procedures are required for the machinery used, and protective measures are required for the operators. No satisfactory solution to these problems has yet been found.